Write wstETH Price Oracle + tests

[nmimran99]

wstETH Oracle

Using stETH price + stETH per wstETH token to determine the price of wstETH in USD

[davekaj]

i rebased on main so i can review

[davekaj]

Hi man I made a few small changes https://github.com/ekonomia-tech/protocol-alpha/pull/88/commits/51333ac149118ffb07680a6ab07dfed542399b36

• imported the solo contract from ERC20AddOns instead of the entire file
• reduced getPrice(address baseToken) to getPrice(address) which effectively ignores that param, which we were not using at all, which allowed us to delete the BadBaseToken event
• deleted a comment that was not relevant (something about ETH NULL ADDRESS)

I approved, if you like the changes, you can merge